Voice mails not being detected during call transfers

Support Help
1

I am using a single prompt voice agent, and I have setup a call transferring mechanism. The call transfers are going through correctly, but the AI does not detect if its a voice mail on the other end of the transferred call. I have also enabled voice mail detection in the call settings but its not working. Help me out.

2

Hey @Muhammad_Azaan Could you please share the relevant Call IDs and Agent ID.

This will help us investigate the issue further.

Thank you.

3

Call IDs : call_3bdba1b1e597055b436772f45ff , call_b49d4addecb25beb06b13513a50
Agent ID: agent_a707c25f3fe0d71dfd4d028860

4

@Muhammad_Azaan Checking it with the team.

5

Hello @Muhammad_Azaan we pulled both calls and the callTransfer tool config. Here’s what’s happening and how to fix it:

  • On both calls the destination answered with a voicemail greeting (“We are unable to take…”), and the agent immediately delivered the warm-transfer whisper, because the transfer was already marked successful from the platform’s point of view.

  • The Voicemail Detection toggle in Call Settings applies to the inbound/origin call, not to the outbound transfer leg — so enabling it there does not prevent whisper-into-voicemail on a warm transfer.

  • Your callTransfer tool has optOutHumanDetection: true set. That flag disables the post-answer voicemail/human classifier on the transfer leg, so the transfer is marked successful regardless of whether a human or voicemail picked up.

Recommended fix (simplest): edit the callTransfer tool on this LLM and set optOutHumanDetection to false. With detection re-enabled, voicemail on the transfer leg will be classified before the whisper is spoken, and the transfer will be treated as failed instead of bridged.

If you want richer voicemail handling (leave a message, retry a fallback number, or cleanly hang up the transfer leg), consider migrating this tool to Agentic Warm Transfer with a dedicated handoff agent.

Thank You

6

I do not see an option that says optOutHumanDetection in the callTransfer function. Can you guide me where to find that

7

Hey @Muhammad_Azaan opt_out_human_detection is a field on the transfer option within general tools (call transfer).

8

image
image673×775 54.8 KB

image
image673×775 46.3 KB

image
image673×775 54.4 KB

I dont see any General Tools or opt_out_human_detection here .

9

Hey @Muhammad_Azaan the field isn’t labeled optOutHumanDetection in the dashboard. It’s exposed as a Yes/No question inside the Warm Transfer settings of your callTransfer tool:

  1. Open your agent → edit the callTransfer tool (the one on agent_a707c25f3fe0d71dfd4d028860 / llm_a200a111a0ebd8279acba890639b).
  2. Scroll to the During Agent Connection section.
  3. Find the question “Is there any internal queue or hold system before an agent answers?” and set it to Yes.

Setting that to Yes is what flips opt_out_human_detection to false under the hood 12 — Retell will then wait for a real person to start speaking before delivering the whisper, and voicemail on the transfer leg will be detected instead of bridged.

(You’ll also see a Wait Time for Agent Answer slider appear once you pick Yes — that’s how long we’ll wait for a human before treating the transfer as failed. Default 30s is fine for most PBX/queue setups.)

Save the agent after the change and give it another test call — let us know if voicemail still slips through.

Thank You